There are two projects described in this proposal. The first concerns purification and characterization of "maturation-promoting factor" (MPF), a cytoplasmic agent appearing at the G2-M transition of the cell cycle of mitotic and meiotic cells. MPF is probably a trigger or central effector of the transition and might better be called "M-phase promoting factor". The cell also contains systems to activate and inactivate MPF at the beginning and end of M phase. We have purified MPF 80-100 fold from unfertilized eggs of Xenopus laevis, a naturally synchronous source of M-phase cells. During further purification,, we will determine whether MPF continues to behave as a single component of 110 20 Kd, and whether the MPF-inactivating agent can be removed. In collaborative work with Dr. M Kirschner, we will attempt to prepare an antibody to MPF. MPF has long been suspected to have protein kinase activity, and we will test this by inactivation of MPF with kinase affinity probes. In addition, the MPF-inactivation system will be partially purified and characterized with regard to its Ca[unreadable]++ and ATP requirement in and vitro. These studies generally concern health problems of cell proliferation and non-proliferation. The second project concerns the formation and function of axial determinants in fertilized eggs of X. laevis. These determinants are thought to control the development of embryonic dorsal structures by cells cleaved from the part of the egg. The formation and function of these agents probably occurs long before gene expression begins; their identity is poorly known, although their importance is clear. We can control their position and extent of formation by experimental means, and will study their formation under controlled conditions. Also, we will study the action of these determinants in causing certain vegetal cells to induce their equatorial neighboring cells to form dorsal mesoderm (the Spemann organizer). These studies concern health problems of vertebrate embryonic development.